Kampo medicines are herbal medicines which originated from Chinese medicine and have been developed in Japan, and crude drugs (galenicals) have been applied to such Kampo medicines from ancient times. Recipes for these crude drugs based on experiences over a long time are described in a number of Chinese classical literatures such as Shang Han Lun and Jin Kui Yao Lue.
However, in the case of Kampo medicine prepared by cutting and decocting crude drugs to thereby extract active ingredients in accordance with these recipes, the preparation of Kampo medicine takes a long time and much labor each time on use. In addition, thus obtained decoctions have characteristic uncomfortable drug odors and tastes and, therefore, cannot be easily taken.
Therefore, in these days, Kampo medicine extract preparations are commonly used in the fields of nonproprietary drugs and ethical drugs and largely contribute to clinical pharmacy, although it is preferable to take the medicines in the form of the above-mentioned decoctions. This is because that these Kampo medicine extract preparations require no procedure for extracting active ingredients and can be easily stored and carried.
These Kampo medicine extract preparations are usually produced by the following method; a crude drug is cut into pieces and extracted with water or an alcohol; the obtained extract solution is concentrated, if required, and then dried to thereby give a powdered extract of the Kampo medicine; and the powdered extract is blended with appropriate fillers (for example, lactose, corn starch, crystalline cellulose) and formulated into a desired dosage forms such as tablets, capsules, powders, fine granules and granules.
Capsules are advantageous in that the content of an active ingredient in each capsule can be accurately controlled and that they can be easily formulated and conveniently carried. It is further advantageous to encapsulate Kampo medicine in hard capsules since the uncomfortable taste, odor and color of a principal agent can be masked and thus a product excellent in appearance can be obtained.
However, when a powdered extract of a Kampo medicine is encapsulated in hard capsules, the pharmaceutical effects of the Kampo medicine cannot be fully achieved, since the dissolution of the content of hard capsules requires a long period of time.
Under these circumstances, it has been required to develop Kampo medicine hard capsules having good dissolution properties.